The <VrfyQuery> element is the SQL query issued for email address verification. You will likely need the placeholders %?U, %?D, and/or %?E. When an email address is not verified, the query should return no rows. When an email address is verified by the query, one row is returned.
The first column is required and holds the canonical form of the requested email address. This may be equal to the requested email address. The second column is optional and returns a unique ID to be used when two-step authentication is performed (two-step is not normally used with DataBase verifiers).
The following snippet shows a very simple <VrfyQuery> element that ignores aliases and unique IDs:
SELECT email FROM emails WHERE email=%?E